1. Technical Field of the Invention
The present invention relates to a storage apparatus. More particularly, the present invention relates to a storage apparatus capable of at least record or reproduction, which is compatible with optical information recording media capable of the concurrent ROM-RAM reproduction.
2. Prior Art
Today, research and development are being actively advanced in terms of high-density recording/reproducing and high-speed accessing for magneto-optical disk memory. FIG. 1 shows a recording medium conforming with the ISO standard and, more specifically, a plan view of a magneto-optical disk as an example. A read-in 1 and a read-out 2 provide ROM information consisting of phase pits according to a principle that pits and projections formed on a polycarbonate substrate are reflected using a reflection film, and information such as specifications of the disk is recorded in them. An apparatus controls conditions for recording/reproducing by reading the information.
The optical depth (pit depth) of the phase pit providing this ROM information is set such that beam intensity modulation during reproduction is maximized. Generally, the depth is set such that the degree of modulation (i.e. the ratio of variation of the beam intensity at a phase pit potion to the beam intensity of a flat portion on which no groove, pit or projection is formed) is 70% or above.
Between the read-in 1 and the read-out 2, there is a user area 3 where a magneto-optical recording film is formed by a sputtering apparatus. A user can record freely information in the user area 3.
FIG. 2 shows a portion of an enlarged plan view of the user area 3. Each land 5 sandwiched respectively by grooves 4 to be tracking guides has phase pits 8 constituting a header portion 6 and a user data portion 7. Information on the header portion 6 consists of a sector mark, a VFO, an ID, etc. according to a sector format.
The user data portion 7 consists of the plane lands 5 and each sandwiched respectively by grooves 4, and records a magneto-optical signal. Recording of a magneto-optical signal is executed by supporting the magnetization inversion using heating by a laser beam on the magneto-optical recording film, inverting the direction of magnetization in response to signals.
FIG. 3 shows a conceptual structure of a cross-section of the user area along the direction of a radius, i.e., along the line A-B in FIG. 2. The user area is constituted by stacking a substrate A made from polycarbonate etc., a dielectric film B, a magneto-optical recording film C made from TbFeCo etc., a dielectric film D, an Al film E and a UV-cured film F as a protecting layer.
FIG. 3 is prepared by amending FIG. 2, according to a recent magneto-optical disk. That is, in FIG. 3, in order to execute magneto-optical recording also in area of the grooves 4, the groove is shown to have a same width as the width of the area of the land 5 in the direction of the radius.
When recorded information is read out, when a weak laser beam is radiated, the orientation of the polarization plane of the laser beam is varied in response to the direction of magnetization of the recording layer under polar Kerr effect, and whether data exist or not is determined from whether the polarized component of a reflected beam at this time is strong or weak. Thereby, reading out of RAM information is possible.
Research and development for utilizing such characteristics of the magneto-optical disk memory are advanced. For example, the Japanese Patent Application Laid-Open Publication No. 1994-202820 and a report in the Journal of the Television Society, vol. 46, No. 10, pp. 1319–1324 (1992) disclose a concurrent ROM (Read Only Memory)-RAM (Random Access Memory) optical disk capable of being reproduced concurrently (hereinafter, referred to as “optical information recording medium”).
Such an optical information recording ROM-RAM medium capable of being reproduced concurrently has a cross-sectional structure along the direction of the radius shown in FIG. 4 and is constituted, as an example, by stacking the substrate A made from polycarbonate etc., the dielectric film B, the magneto-optical recording film C made from TbFeCo etc., the dielectric film D, the Al film E and the UV-cured film F as a protecting layer.
In the optical information recording medium having such a structure, as shown in FIG. 5, ROM information is recorded fixedly by phase pits PP and RAM information is recorded on rows of the phase pits PP with magneto-optical recording OMM. A cross-section along the A-B line in the direction of the radius in FIG. 5 coincides with the view of FIG. 4.
In an example shown in FIG. 5, grooves shown in FIG. 2 and FIG. 3 are not provided since the rows of phase pit PP are tracking guides in this case.
For such an optical information recording medium having the ROM information and the RAM information on the same recording surface, there are many problems for reproducing concurrently the ROM (for reading out only) information consisting of the phase pits PP and the RAM (writable/rewritable) information consisting of Optical Magnetic Memory (OMM). First, in order to reproduce the RAM information stably with the ROM information, it is necessary to reduce the optical intensity modulation occurring when the ROM information is being read out.
Thus, in the above conventional technique, an optical intensity modulation signal of ROM information read-out is reduced by negative feedback to a driving laser (hereinafter, referred to as “MPF [Modulated Power Feedback]).
However, when the degree of the optical intensity modulation is high, the above conventional technique is not satisfactory. That is, the reproducing margin is also reduced if the optical intensity modulation is reduced too much.
Further, an example of configuration shown in FIG. 6, described in the Japanese Patent Application Laid-Open Publication Nos. 1989-166350 and 1995-65375 and in the above report of Journal of the Television Society, is known as a conventional storage apparatus for the aforementioned optical information recording medium with MPF.
In a brief description of such a configuration, laser beam, a light beam emitted from a semiconductor laser diode LD that serves as a light source, is converted to parallel luminous flux by a collimator lens 10.
Next, the converted parallel luminous flux enters a polarizing beam splitter 11. After passing through the polarizing beam splitter 11, the flux is reduced roughly to the diffraction limit by an objective lens 16 and irradiated to an optical information recording medium 17. The optical information recording medium 17 is rotated by a motor 18. Further, the luminous flux reflected by the optical information recording medium 17 enters the polarizing beam splitter 11 again via the objective lens 16, where the flux is reflected and guided into a servo optical system and a recording information detection system.
That is, light from the optical information recording medium 17 reflected by the polarizing beam splitter 11 enters a second polarizing beam splitter 19, and transmitted light therefrom enters the servo optical system, whereas light reflected by the second polarizing beam splitter 19 enters the recording information detection system.
Transmitted light from the second polarizing beam splitter 19 enters a 4-part photodetector 22 via a condensing lens 20 and a cylindrical lens 21 in the servo optical system, and the light undergoes photoelectric conversion in the 4-part photodetector 22.
Using the output of the 4-part photodetector 22 following photoelectric conversion, focus error sensing (FES) is conducted by a generator circuit 23 of astigmatic focus error detection. At the same time, track error sensing (TES) is conducted by a generator circuit 24 of push-pull method.
Detected focus error signal (FES) and track error signal (TES) are used for tracking feedback control via an FES/TES actuator 37.
In the recording information detection system, on the other hand, reflected laser light enters a 2-beam wollaston 26 splitting into two beams, orthogonal to each other, based on the polarization characteristic of reflected laser light that changes according to the orientation of the magneto-optical records on the optical information recording medium 17. The beams enter a 2-part photodetector 28 via a condensing lens 27, where each undergoes photoelectric conversion.
On the one hand, two electric signals resulting from photoelectric conversion in the 2-part photodetector 28 are added together by a summing amplifier 29 and further guided into an LD controller 100, whereas, on the other hand, they are subtracted from each other by a subtracting amplifier 30 to be a RAM readout signal (RAM).
The output of the summing amplifier 29 guided into the LD controller 100 is output from the LD controller 100 as LD drive current. Monitoring this drive current allows detection of ROM signal.
In detecting ROM and RAM signals, at this time, a circuit is added in the configuration of the LD controller 100 shown in FIG. 7 to superpose a high-frequency signal 101 at several hundred MHz range on the LD drive current, thus eliminating noise caused by returned light from the optical information recording medium 17.
For this reason, an LD drive circuit (not shown in the figure) provided in the LD must be capable of pass radio drive current from the LD controller 100. During ROM signal detection, the signal passes through an amplifier 102 for detection to minimize changes in frequency characteristic of the LD drive circuit. However, complete elimination of effects on the LD circuit frequency characteristic is difficult. Therefore, the configuration of the conventional storage apparatus shown in FIG. 6 faces a problem of ROM and RAM signal characteristic degradation.